1. Field of the Invention
This invention relates to a wafer conveying system in a clean room.
2. Description of the Prior Art
FIG. 4 shows one example of the arrangement of equipments installed in a clean room in a conventional semiconductor processing system. In FIG. 4, reference numeral 91 designates a semiconductor processing equipment which incorporates, for instance, a reaction furnance for subjecting wafers to surface treatment; 92, a wafer inspecting equipment; 93, a self-running type cassette placing robot for conveying cassettes; 97, a cassette washing equipment; 94, a wafer storechamber; 94B and 94A, a carry-in gate and a carry-out gate of the wafer storechamber 94, respectively; and 95, a product conveying system (such as a linear-motor-type track) for conveying products between manufacturing lines.
In the semiconductor processing system, cassettes conveyed by the conveying equipment are unloaded at the wafer storechamber 94 and stored on a predetermined shelf therein. In this case, a cassette 100 is stored which is set in a portable container 300. A stacker crane 96 is provided in the wafer storechamber 94. When a cassette 100 is carried in the carry-in gate 94B, the stacker crane 96 is operated to store the cassette 100 on a predetermined shelf. The cassette 100, which is set in a container 300 in the wafer storechamber 94 is delivered to the carry-out gate 94A by the stacker crane 96. Thereupon, the self-running type wafer placing robot 93 operates as follows: That is, it delivers the cassette 100 set in the container 300 to the semiconductor processing equipment 91 as it is, or delivers to the wafer inspecting equipment 92 or the wafer storechamber 94 the container 300 containing the cassette in which wafers processed have been stored.
In the conventional semiconductor manufacturing system, the cassettes 100 each containing a plurality of wafers (for instance twenty-five (25) wafers) are moved from equipment to equipment one at a time.
On the other hand, recently the demand for ASIC (application specific IC) has been increased, and the number of wafers manufactured per lot has been decreased. Therefore, sometimes the number of wafers in the cassette is one or two. Accordingly, in the conventional semiconductor manufacturing system employing the above-described conveying system, the cassette each containing one or two wafers are conveyed. Thus, in the conventional semiconductor manufacturing system, the wafer conveying efficiency is considerably low.